In recent years, automobile weight reduction is promoted due to an environmental issue particularly in the automobile industry. CAE analysis is an essential technology for the design of the automotive body (for example, see Japanese Unexamined Patent Application Publication No. 2004-171144). Also, it is known that the result of the CAE analysis is largely affected by mechanical characteristic values of a material to be input (metal sheet, for example, steel sheet). In press-forming analysis, YS (yield strength), TS (tensile strength), and r value (Lankford value) mainly contribute to the analysis. In stiffness analysis, an elasticity coefficient such as a Young's modulus contributes to the analysis in proportion to a displacement obtained by the analysis. In crashworthiness analysis, metal sheet strength values such as YS and TS largely contribute to the analysis.
Meanwhile, there may be a metal sheet, the mechanical characteristic of which has large in-plane anisotropy (the metal sheet is called anisotropic metal sheet). In particular, it is known that a metal sheet manufactured by rolling has a variation in characteristic from 2% to 50% in view of a characteristic variation range calculated by (maximum−minimum)/maximum×100, in the rolling direction (L direction), the direction orthogonal thereto (C direction), and the 45° direction (D direction).
In the CAE analysis, if the analysis subject is a metal sheet, the mechanical characteristic of which is constant in a planar direction (isotropic metal sheet), a problem caused by a direction does not occur. However, in an anisotropic metal sheet, if a mechanical characteristic value in a direction different from a major deformed direction of the metal sheet is input, the calculation result may be different from the calculation result without anisotropy.
Hence, for the anisotropic metal sheet, information relating to the in-plane anisotropy of the mechanical characteristic (hereinafter referred to as anisotropy information) is required to be set for each element of the analysis model, which is formed by dividing the analysis subject into a plurality of elements.
The anisotropy information provides a mechanical characteristic value corresponding to a desirable direction. The anisotropy information is provided while a certain direction (for example, the L direction, the C direction, or a direction between these directions) serves as a reference direction, as correspondence information between an azimuth angle with respect to the reference direction and the mechanical characteristic. The anisotropy information can be previously provided in the form of a table or a function. The table or the function may be stored and used through an analysis program.
The relationship between the reference direction and the azimuth angle is described more specifically by using the above-described rolled metal sheet as an example. If it is assumed that the C direction is the reference direction (azimuth angle 0°), the mechanical characteristic at the azimuth angle of 90° is the mechanical characteristic in the L direction, and the mechanical characteristic at the azimuth angle of 45° is the mechanical characteristic in the D direction. Also, if it is assumed that the L direction is the reference direction, the mechanical characteristic at the azimuth angle of 90° with respect to the reference direction is the mechanical characteristic in the C direction orthogonal to the L direction with reference to the table.
The reference direction is indicated by a single arrow in each element on the analysis image (for example, see FIG. 4). The reference direction is fixed to each element of the analysis model. If each element moves and rotates, the reference direction moves and rotates similarly.
As described above, if the aforementioned anisotropic metal sheet is used for an automotive body in the automobile industry, the anisotropy information is required to be set for the analysis model in the CAE analysis.
However, when the automotive body is designed, in many cases, at first, the shape of the automotive body is determined, the analysis model is created for the shape, and then the stiffness analysis is executed.
The analysis model based on the shape is not provided with the anisotropy information. Hence, correct analysis cannot be executed even if the stiffness analysis is executed in this state. Therefore, in the past, the anisotropy information has been input according to guesswork for each element of the analysis model to set the anisotropy information for the analysis model in preparation for the analysis.
However, the number of elements used for the analysis model of the current automotive body is about 300,000 to 500,000. It is extremely difficult to manually input the anisotropy information for all elements.
Also, an actual press-formed panel has a complex shape with curves. The movement and rotation of each element by press-forming cannot be correctly recognized according to such guesswork, and it is difficult to properly input the anisotropy information.
Thus, even if the anisotropy information is input according to the guesswork of the person, the result of the stiffness analysis obtained thereafter may frequently mismatch the result of the stiffness test or crashworthiness test of the corresponding actual press-formed panel.
Also, the analysis model in which only the above-described shape is modeled does not have set therein the variation information of the sheet thickness by press-forming, that is, the sheet thickness information.
However, the sheet thickness information is very important to execute the CAE analysis more correctly. For example, since a structure body using a sheet, represented by the automotive body, is press-formed, the sheet thickness may be different from the original sheet thickness depending on the position of the panel. For example, the thicknesses of an R portion and a bulging portion are decreased, and the thickness of a wrinkled portion is increased.
If the sheet thickness is both decreased and increased as described above, the stiffness and crashworthiness characteristic of the portions are decreased and increased. Hence, to execute the correct CAE analysis, analysis has been requested to be executed with regard to the sheet thickness information.
It could therefore be helpful to provide a setting method of anisotropy information and sheet thickness information correctly with a markedly reduced calculation time without manual input.